It is important to secure a stable throughput with the growing needs for a larger data amount and a faster data transmission in these days. In the 3rd Generation Partnership Project Long Term Evolution (3GPP-LTE) that is a new communication scheme for mobile communications, a channel bandwidth is extended up to 20 MHz. Extension of a channel bandwidth tends to increase the in-band ripple deviation (hereinafter, abbreviated as “ripple deviation”) inherent in a high-frequency device such as a duplexer. The increase of the ripple deviation causes reduction of the Error Vector Magnitude (EVM) and thus reduces the throughput.
FIG. 1 illustrates an example of frequency characteristics of a duplexer that is used in a wireless communication device mounted on a communication terminal device (hereinafter, abbreviated as “communication terminal”) such as a mobile phone. In the example, ripple deviations occur in the transmission bandwidth of 1920 to 1980 MHz. The ripple deviations vary depending on each individual duplexer due to the temperature change, the variation in the elements, the difference of manufacturers, the difference of models even in the same manufacture, or the like. It is difficult to further improve the performance of the duplexer itself in order to reduce the ripple deviations because it increases the production cost.
Conventionally, to reduce the effect of ripple deviations to a transmission signal, a technique for previously correcting the voltage level of the transmission signal before being input to the duplexer with a correction value for negating the ripple deviation (hereinafter, abbreviated as “correction value”) has been used. Conventionally, based on the correction values for as many wireless communication devices as possible, the average value of the correction values is stored in the memories of wireless communication devices as the correction value of the individual wireless communication device at the experimental stage of a wireless communication device. Then, when the wireless communication is in a communication state, the correction value stored in the memory corrects the voltage level of the transmission signal.
Related-art examples are described, for example, in Japanese Laid-open Patent Publication No. 2004-235966 and Japanese Laid-open Patent Publication No. 2006-186690.
Because the correction value stored in the memory at the experimental stage of a wireless communication device as described above is a fixed value, it is difficult to follow the temperature change. On the contrary, when the correction values according to the temperatures are stored in the memory in consideration of the temperature change, the storage capacity of the memory becomes large and thus the device scale of the wireless communication device becomes large. Further, in this case, since it is preferable to detect the temperature of the wireless communication device, the device structure of the wireless communication device becomes complicated. Further, because the correction value stored in the memory is conventionally an average value of a plurality of wireless communication devices, it is difficult to completely correct the ripple deviations that are different from each other at each duplexer.